A touch panel for touch input is widely applied in an image display panel for use in an optical display device for televisions, mobile phones, personal digital assistances and others, etc. There are various types of touch panels, such as a resistive (resistive film) type and a capacitive type. The resistive touch panel comprises two upper and lower transparent electrodes such as ITO electrodes, wherein it is configured such that, when the upper electrode is pressed by a finger or the like, the two electrodes come into press contact with each other to cause current to pass therebetween, and a resulting generated current is detected by a sensor, thereby detecting a pressed position. The capacitive touch panel is configured such that, when a user's finger touches a window of the touch panel, a capacitance is formed between the finger and a (transparent) electrode of the touch panel, and a resulting change in capacitance is used to detect a touched position.
According to a configuration of an electrode, the capacitive touch panel can be classified into a surface capacitive type in which a sensor electrode is formed as a single sheet, and a projected capacitive type in which a sensor electrode consists of a group of X-electrode lines and a group of Y-electrode lines which are arranged to intersect each other to form a grid pattern. The projected capacitive touch panel is further classified into a self-capacitance detection type in which the X-axis electrode lines and Y-axis electrodes are scanned independently to detect individual capacitance changes, and a mutual-capacitance detection type in which the group of X-electrode lines and the group of Y-electrode lines are configured, respectively, as a transmitting electrode and a receiving electrode, and a capacitance change at each adjacent position between the X- and Y-electrode lines is detected.
As compared to the self-capacitance detection type, the mutual-capacitance detection type is considered to be advantageous in that: there is no unclarity (uncertainty) in detection of coordinates even in particular usage such as multi-touch, because it is configured to detect a capacitance change at each intersection between the X- and Y-electrode lines; the detection can be performed in an easy and high-speed manner, because it is configured to detect only a coupling capacitance while separating input and output terminals from each other; and it is possible to reduce a required memory capacity, and ease a burden on hardware, and gust is less likely to occur, because the detection is performed by scanning in either one of two axial direction.
As regards such a capacitive touch panel, higher performance is required. In particular, there is a need for a capacitive touch panel with enhanced detection sensibility.
Heretofore, there have been made various attempts to improve a capacitive touch panel to have higher performance, with a focus on permittivities of various portions constituting the capacitive touch panel.
JP 2009-37373A relates a technique intended to suppress the occurrence of erroneous input due to a change in capacitance of a sensor electrode adjacent to a desired sensor electrode, and discloses providing a plurality of first blocks each disposed in contact with respective central regions of a plurality of sensor electrodes, and a plurality of second blocks each disposed between adjacent ones of the first blocks, wherein the second block has a dielectric constant less than that of the first block.
JP 2009-70191A relates to a technique intended to provide a capacitance sensor having an extremely fine electrode pattern formed with high degree of accuracy, and discloses providing a dielectric constant adjusting layer between a first transparent layer having a first electrode pattern arranged on a surface thereof, and a second transparent layer having a second electrode pattern arranged on a surface thereof.
JP 2010-176571A relates a technique intended to realize a projected capacitive touch panel capable of enhancing coordinate detection system, and disclosed that a dielectric constant of an adhesive existing between a first electrode pattern and a second electrode pattern has a given relationship with a dielectric constant of the first and second electrode patterns.